1. Field of the Invention
The present invention relates to a system and method for increasing the viable wear life of friction materials used on mechanical stamping hydraulic clutch/brake units by controlling the hydraulic clutch pressure to compensate for clutch wear.
2. Description of the Related Art
Existing systems use steady state hydraulic pressure to actuate the clutch. Accumulator units are used to augment the flow capabilities of the pump during heavy usage periods. No control system is in place to selectively and dynamically change the clutch pressure. As friction material wear occurs, mechanical adjustments for wear are required or the friction material elements must be replaced.
Mechanical presses, such as straight side presses and gap frame presses for stamping and drawing, generally include a frame having a crown and bed and a slide supported within the frame for reciprocating motion toward and away from the bed. The slide is typically driven by a crankshaft having a connecting arm connected to the slide, to which is mounted the upper die. Rotation of the crankshaft moves the connecting rods to effect straight reciprocating motion of the slide. The lower die is conventionally mounted to a bolster which, in turn, is connected to the bed.
Such mechanical presses are widely used for blanking and drawing operations and vary substantially in size and available tonnage depending on their intended use.
The primary apparatus for storing mechanical energy in a press is the flywheel. The flywheel and flywheel bearing are normally axially mounted on either the driveshaft, crankshaft, or the press frame by use of a quill. The flywheel is typically mounted at one end of the crankshaft and connected by a belt to the output pulley of a motor such that when the motor is energized, the massive flywheel rotates continuously. The motor replenishes the energy that is lost or transferred from the flywheel during press operations. When the clutch engages the flywheel to transmit rotary motion of the flywheel to the crankshaft, the flywheel drops in speed as the press driven parts are brought up to press running speed.
Continuous and repetitive clutch engagement and release causes the clutch friction material to wear. The clutch friction material abrades away and after a certain amount of wear, the clearance between the clutch and the flywheel grows. As the clearance grows, the time it takes for the clutch and flywheel to engage increases, thus reducing press cycle time.
According to the present invention, a method and apparatus are described for increasing the viable wear life of friction materials used on mechanical stamping hydraulic clutch/brake units by controlling the hydraulic clutch pressure to compensate for clutch wear.
Disclosed is a system designed to use a hydraulic clutch modulation system that allows control of the clutch engagement characteristics to improve the clutch reaction time and to allow for full utilization of more thickness of the clutch friction material without having to replace the friction pads or adjust the clutch mechanism.
Through the use of a hydraulic valve, servo valve and/or other control system, the clutch hydraulic pressure can be selectively and dynamically increased during clutch actuation and returned to a normal clutch pressure setting prior to beginning the stamping operation. Increasing the pressure during clutch actuation means that the clutch will fill faster with oil and also translate faster axially to engage with the flywheel. Improvements in clutch responsiveness can result in up to two or three times the serviceable life of the friction wear pads before removal of the pads is required.
Axial clearances in the clutch unit increase as the friction material wears. Increasing axial clearances results in slower response times when engaging the hydraulic clutch since additional time is required to translate the hydraulic clutch components through the clearances. By controlling the pressure and flow characteristics of the oil into the clutch, the clutch actuation responsiveness can be maintained at original specifications as the friction material wears and clearances increase.
The system as used on a mechanical stamping hydraulic press includes a hydraulically actuated clutch with an oil supply system, and a control package to operate the hydraulic system. On clutch engagement, the control package will cause the hydraulic supply unit to supply oil under elevated pressure to the clutch, resulting in rapid clutch engagement. Once engagement is completed the control system will cause the hydraulic supply unit to return to a normal operating pressure, sufficient to maintain the clutch at the required operating torque levels.
The invention, in one form thereof, includes a dual pressure pump system having the ability to operate the pump at either a high pressure or low pressure and means for applying working pressure from said dual pressure pump system such that a higher pressure is applied during clutch engagement.
An advantage of the present invention is the clutch engagement time is reduced allowing for greater operator productivity and safety.
Another advantage of the present invention is that improvements in clutch responsiveness can result in up to two to three times the serviceable life of the friction wear pads before service is required.
Another advantage of the present invention is that since the clutch is operating at normal pressures and the high pressure spike is used only during clutch engagement, no clutch design torques are exceeded.
A further advantage of the invention is that existing presses may be quickly retrofitted with this design.